Solids of this type are known, for example, from the Japanese published specification JP-A-53-011 982 or from DE-A-26 23 693.
The solid described in JP-A-53-011 982 is magnesium oxide, zinc oxide, silica gel, magnesium hydroxide, aluminum silicate or magnesium silicate which has been reacted with triethylaluminum, tri-n-octylaluminum, diethylaluminum hydride or isobutylaluminum dihydride at from 50 to 100° C. in hexane or decane. The resulting solids or supported aluminum compounds are used as activators for Phillips catalysts comprising chromium oxide in ethylene polymerization. For the aluminum alkyl compounds to be able to display their known activation effect, they have to react with the chromium oxide of the Phillips catalysts. It is therefore a physical requirement that the solid of JP-A-53-011 982 contains only a very small amount, if any, of immobilized aluminum alkyls, since otherwise the mass transfer between the solid and the Phillips catalyst which is essential for activation would no longer take place. Nothing is said in JP-A-53-011 982 about a purifying effect of the solid.
The solid described in DE-A-26 23 693 is likewise based on supports such as alumina, hydrated alumina, silicic acid, aluminum silicate and magnesium silicate and, in addition, calcium carbonate, magnesium carbonate or a polyolefin powder which have been impregnated with at least one liquid aluminum alkyl compound having a vapor pressure of less than 1 mm/80° C., e.g. tri-n-octylaluminum. These solids are used as cocatalysts for the (co)polymerization of α-monoolefins in the gas phase by means of Ziegler or Phillips catalysts comprising transition metals.
EP-A-560128 discloses a solid which contains metal alkyl groups and in which the metal alkyls are all bound to the surface of the support. Although this has the advantage that it reduces the interactions with the polymerization catalyst, the supported metal alkyl compounds obtained in this way have, like all other previously known solids comprising metal alkyls, the disadvantage that they easily become conglutinated when being metered into the reaction, in particular when using long, narrow lines, and are therefore not very suitable for metering into a gas-phase fluidized-bed reactor.